diff --git a/.Rbuildignore b/.Rbuildignore
index f92ee80..33dfb18 100644
--- a/.Rbuildignore
+++ b/.Rbuildignore
@@ -6,3 +6,4 @@
 ^inst/trash$
 ^inst/RDS$
 ^cran-comments\.md$
+^CRAN-SUBMISSION$
diff --git a/DESCRIPTION b/DESCRIPTION
index d7773bb..a67a93d 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: symbolicQspray
 Title: Multivariate Polynomials with Symbolic Parameters in their Coefficients
-Version: 1.0.0
+Version: 1.0.0.9000
 Authors@R: 
     person("Stéphane", "Laurent", , "laurent_step@outlook.fr", role = c("aut", "cre"))
 Description: Introduces the 'symbolicQspray' objects. Such an object
@@ -16,9 +16,10 @@ Description: Introduces the 'symbolicQspray' objects. Such an object
 License: GPL-3
 URL: https://github.com/stla/symbolicQspray
 BugReports: https://github.com/stla/symbolicQspray/issues
+Remotes: stla/qspray, stla/ratioOfQsprays
 Depends:
-    qspray (>= 3.0.0),
-    ratioOfQsprays
+    qspray (>= 3.0.0.9000),
+    ratioOfQsprays (>= 1.0.0.9000)
 Imports: 
     gmp,
     methods,
diff --git a/NAMESPACE b/NAMESPACE
index 8c25d00..ba32f85 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -24,6 +24,7 @@ exportMethods(changeVariables)
 exportMethods(compactSymmetricQspray)
 exportMethods(getCoefficient)
 exportMethods(getConstantTerm)
+exportMethods(involvedVariables)
 exportMethods(isConstant)
 exportMethods(isQone)
 exportMethods(isQzero)
@@ -48,6 +49,7 @@ importFrom(qspray,compactSymmetricQspray)
 importFrom(qspray,evalQspray)
 importFrom(qspray,getCoefficient)
 importFrom(qspray,getConstantTerm)
+importFrom(qspray,involvedVariables)
 importFrom(qspray,isConstant)
 importFrom(qspray,isQone)
 importFrom(qspray,isQzero)
diff --git a/R/internal.R b/R/internal.R
index ee7ad7f..ce64b2a 100644
--- a/R/internal.R
+++ b/R/internal.R
@@ -115,8 +115,8 @@ arity <- function(qspray) {
 }
 
 powersMatrix <- function(qspray) {
-  n <- arity(qspray)
-  if(n == -Inf) {
+  n <- numberOfVariables(qspray)
+  if(n == 0L) {
     matrix(NA_integer_, 0L, 0L)
   } else {
     do.call(rbind, lapply(qspray@powers, grow, n = n))
diff --git a/R/queries.R b/R/queries.R
index 048d978..68e3498 100644
--- a/R/queries.R
+++ b/R/queries.R
@@ -2,6 +2,7 @@
 NULL
 
 setGeneric("numberOfVariables")
+setGeneric("involvedVariables")
 setGeneric("numberOfTerms")
 setGeneric("getCoefficient")
 setGeneric("getConstantTerm")
@@ -14,13 +15,14 @@ setGeneric("isQone")
 #' @aliases numberOfVariables,symbolicQspray-method
 #' @docType methods
 #' @importFrom qspray numberOfVariables
-#' @title Number of variables in a 'symbolicQspray' polynomial
+#' @title Number of variables of a 'symbolicQspray' polynomial
 #' @description Number of variables involved in a \code{symbolicQspray} object.
 #'
 #' @param x a \code{symbolicQspray} object
 #'
 #' @return An integer.
 #' @export
+#' @seealso \code{\link{involvedVariables}}.
 #' @note The number of variables in the \code{symbolicQspray} object
 #'   \code{Qlone(d)} is \code{d}, not \code{1}.
 setMethod(
@@ -30,6 +32,39 @@ setMethod(
   }
 )
 
+#' @name involvedVariables
+#' @aliases involvedVariables,symbolicQspray-method
+#' @docType methods
+#' @importFrom qspray involvedVariables
+#' @title Variables involved in a 'symbolicQspray' polynomial
+#' @description Variables involved in a \code{symbolicQspray} object.
+#'
+#' @param x a \code{symbolicQspray} object
+#'
+#' @return A vector of integers. Each integer represents the index of a
+#'   variable involved in \code{x}.
+#' @export
+#' @seealso \code{\link{numberOfVariables}}.
+#' @examples
+#' a1 <- qlone(1); a2 <- qlone(2)
+#' X <- Qlone(1); Z <- Qlone(3)
+#' Qspray <- (a1/a2)*X^2 + (a1/(a1+a2))*X*Z + a2^2/a1
+#' involvedVariables(Qspray) # should be c(1L, 3L)
+setMethod(
+  "involvedVariables", "symbolicQspray",
+  function(x) {
+    if(isConstant(x)) {
+      integer(0L)
+    } else {
+      M <- powersMatrix(x)
+      tests <- apply(M, 2L, function(col) {
+        any(col != 0L)
+      })
+      which(tests)
+    }
+  }
+)
+
 #' @name numberOfTerms
 #' @aliases numberOfTerms,symbolicQspray-method
 #' @docType methods
@@ -54,27 +89,25 @@ setMethod(
 #' @docType methods
 #' @importFrom qspray getCoefficient
 #' @title Get a coefficient in a 'symbolicQspray' polynomial
-#' @description Get the coefficient corresponding to the given sequence of
-#'   exponents.
+#' @description Get the coefficient of the term with the given monomial.
 #'
 #' @param qspray a \code{symbolicQspray} object
-#' @param exponents a vector of exponents
+#' @param exponents a vector of exponents, thereby defining a monomial;
+#'   trailing zeros are ignored
 #'
-#' @return The coefficient as a \code{ratioOfQsprays} object.
+#' @return The coefficient, \code{ratioOfQsprays} object.
 #' @export
-#' @importFrom gmp as.bigq
-#' @importFrom ratioOfQsprays showRatioOfQspraysOption<-
+#' @importFrom ratioOfQsprays showRatioOfQspraysOption<- as.ratioOfQsprays
 #'
 #' @examples
-#' library(qspray)
-#' x <- qlone(1)
-#' y <- qlone(2)
-#' p <- 2*x^2 + 3*y - 5
-#' getCoefficient(p, 2)       # coefficient of x^2
+#' a1 <- qlone(1); a2 <- qlone(2)
+#' X <- Qlone(1); Y <- Qlone(2)
+#' p <- 2*(a1/a2)*X^2 + (a1/(a1+a2))*Y + a2^2/a1
+#' getCoefficient(p, 2)       # coefficient of X^2
 #' getCoefficient(p, c(2, 0)) # same as getCoefficient(p, 2)
-#' getCoefficient(p, c(0, 1)) # coefficient of y (= x^0.y^1)
+#' getCoefficient(p, c(0, 1)) # coefficient of Y (because Y=X^0.Y^1)
 #' getCoefficient(p, 0)       # the constant term
-#' getCoefficient(p, 3)       # coefficient of x^3
+#' getCoefficient(p, 3)       # coefficient of X^3
 setMethod(
   "getCoefficient", c("symbolicQspray", "numeric"),
   function(qspray, exponents) {
diff --git a/man/getCoefficient.Rd b/man/getCoefficient.Rd
index b0f8f1f..5a95a2f 100644
--- a/man/getCoefficient.Rd
+++ b/man/getCoefficient.Rd
@@ -11,23 +11,22 @@
 \arguments{
 \item{qspray}{a \code{symbolicQspray} object}
 
-\item{exponents}{a vector of exponents}
+\item{exponents}{a vector of exponents, thereby defining a monomial;
+trailing zeros are ignored}
 }
 \value{
-The coefficient as a \code{ratioOfQsprays} object.
+The coefficient, \code{ratioOfQsprays} object.
 }
 \description{
-Get the coefficient corresponding to the given sequence of
-  exponents.
+Get the coefficient of the term with the given monomial.
 }
 \examples{
-library(qspray)
-x <- qlone(1)
-y <- qlone(2)
-p <- 2*x^2 + 3*y - 5
-getCoefficient(p, 2)       # coefficient of x^2
+a1 <- qlone(1); a2 <- qlone(2)
+X <- Qlone(1); Y <- Qlone(2)
+p <- 2*(a1/a2)*X^2 + (a1/(a1+a2))*Y + a2^2/a1
+getCoefficient(p, 2)       # coefficient of X^2
 getCoefficient(p, c(2, 0)) # same as getCoefficient(p, 2)
-getCoefficient(p, c(0, 1)) # coefficient of y (= x^0.y^1)
+getCoefficient(p, c(0, 1)) # coefficient of Y (because Y=X^0.Y^1)
 getCoefficient(p, 0)       # the constant term
-getCoefficient(p, 3)       # coefficient of x^3
+getCoefficient(p, 3)       # coefficient of X^3
 }
diff --git a/man/involvedVariables.Rd b/man/involvedVariables.Rd
new file mode 100644
index 0000000..b232379
--- /dev/null
+++ b/man/involvedVariables.Rd
@@ -0,0 +1,29 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/queries.R
+\docType{methods}
+\name{involvedVariables}
+\alias{involvedVariables}
+\alias{involvedVariables,symbolicQspray-method}
+\title{Variables involved in a 'symbolicQspray' polynomial}
+\usage{
+\S4method{involvedVariables}{symbolicQspray}(x)
+}
+\arguments{
+\item{x}{a \code{symbolicQspray} object}
+}
+\value{
+A vector of integers. Each integer represents the index of a
+  variable involved in \code{x}.
+}
+\description{
+Variables involved in a \code{symbolicQspray} object.
+}
+\examples{
+a1 <- qlone(1); a2 <- qlone(2)
+X <- Qlone(1); Z <- Qlone(3)
+Qspray <- (a1/a2)*X^2 + (a1/(a1+a2))*X*Z + a2^2/a1
+involvedVariables(Qspray) # should be c(1L, 3L)
+}
+\seealso{
+\code{\link{numberOfVariables}}.
+}
diff --git a/man/numberOfVariables.Rd b/man/numberOfVariables.Rd
index 9e010ae..644029f 100644
--- a/man/numberOfVariables.Rd
+++ b/man/numberOfVariables.Rd
@@ -4,7 +4,7 @@
 \name{numberOfVariables}
 \alias{numberOfVariables}
 \alias{numberOfVariables,symbolicQspray-method}
-\title{Number of variables in a 'symbolicQspray' polynomial}
+\title{Number of variables of a 'symbolicQspray' polynomial}
 \usage{
 \S4method{numberOfVariables}{symbolicQspray}(x)
 }
@@ -21,3 +21,6 @@ Number of variables involved in a \code{symbolicQspray} object.
 The number of variables in the \code{symbolicQspray} object
   \code{Qlone(d)} is \code{d}, not \code{1}.
 }
+\seealso{
+\code{\link{involvedVariables}}.
+}