Add the function "is_singleton"

src-base/interval_base.ml

@@ -49,6 +49,7 @@ module type T = sig
 
   val compare_f: t -> number -> int
   val belong : number -> t -> bool
+  val is_singleton : t -> bool
   val is_bounded : t -> bool
   val is_entire : t -> bool
   val equal : t -> t -> bool
@@ -431,6 +432,8 @@ module I = struct
 
   let belong x {low; high} = low <= x && x <= high
 
+  let is_singleton {low; high} = (low = high)
+
   let is_bounded {low; high} =
     neg_infinity < low && high < infinity
 

src-base/interval_base.mli

@@ -117,6 +117,11 @@ module type T = sig
   val belong : number -> t -> bool
   (** [belong x a] returns whether [x] ∈ [a]. *)
 
+  val is_singleton : t -> bool
+  (** [is_singleton x] says whether [x] is a ingleton i.e., the two
+     bounds of [x] are equal.
+     @since 1.6 *)
+
   val is_bounded : t -> bool
   (** [is_bounded x] says whether the interval is bounded, i.e.,
       -∞ < [inf(x)] and [sup(x)] < ∞.