diff --git a/9cc-memo.xmind b/9cc-memo.xmind
index e12ceb1..b29505d 100644
Binary files a/9cc-memo.xmind and b/9cc-memo.xmind differ
diff --git a/9cc.c b/9cc.c
index 2a67809..531597d 100644
--- a/9cc.c
+++ b/9cc.c
@@ -94,7 +94,7 @@ bool at_eof()
 // 新しいトークンを作成してcurに繋げる
 Token *new_token(TokenKind kind, Token *cur, char *str)
 {
-  Token *tok = calloc(1, sizeof(Token)); //? callocの仕様を知りたい
+  Token *tok = calloc(1, sizeof(Token));
   tok->kind = kind;
   tok->str = str;
   cur->next = tok;
@@ -119,7 +119,7 @@ Token *tokenize()
     }
 
 //    if (*p == '+' || *p == '-' || *p == '*' || *p == '/' || *p == '(' || *p == ')' )
-    if (strchr("+-*/()",*p)) //strchrってどういう関数?
+    if (strchr("+-*/()",*p)) 
     {
       cur = new_token(TK_RESERVED, cur, p++);
       continue;
@@ -185,6 +185,7 @@ Node *new_node_num(int val)
 
 Node *expr();
 Node *mul();
+Node *unary();
 Node *primary();
 
 // expr    = mul ("+" mul | "-" mul)*
@@ -203,22 +204,32 @@ Node *expr()
   }
 }
 
-// mul     = primary ("*" primary | "/" primary)*
+// mul     = unary ("*" unary | "/" unary)*
 // *,/ : 左結合演算子
 Node *mul()
 {
-  Node *node = primary();
+  Node *node = unary();
   for (;;)
   {
     if (consume('*'))
-      node = new_node(ND_MUL, node, primary());
+      node = new_node(ND_MUL, node, unary());
     else if (consume('/'))
-      node = new_node(ND_DIV, node, primary());
+      node = new_node(ND_DIV, node, unary());
     else
       return node;
   }
 }
 
+// unary  = unary   = ("+" | "-")? primary
+Node *unary()
+{
+  if (consume('+'))
+      return primary();
+  if (consume('-'))
+    return new_node(ND_SUB, new_node_num(0),primary());
+  return primary();
+}
+
 // primary = num | "(" expr ")"
 Node *primary()
 {
@@ -246,7 +257,7 @@ void gen(Node *node)
   if (node->kind == ND_NUM )
   {
     printf("  push %d\n", node->val);
-    return; //空returnはどう解釈される?
+    return;
   }
 
   gen(node->lhs);
diff --git "a/images/\346\226\207\346\263\225\343\201\256\350\250\230\350\277\260\346\226\271\345\274\217\343\201\250 \345\206\215\345\270\260\344\270\213\351\231\215\346\247\213\346\226\207\350\247\243\346\236\220.png" "b/images/\346\226\207\346\263\225\343\201\256\350\250\230\350\277\260\346\226\271\345\274\217\343\201\250 \345\206\215\345\270\260\344\270\213\351\231\215\346\247\213\346\226\207\350\247\243\346\236\220.png"
new file mode 100644
index 0000000..32d06f7
Binary files /dev/null and "b/images/\346\226\207\346\263\225\343\201\256\350\250\230\350\277\260\346\226\271\345\274\217\343\201\250 \345\206\215\345\270\260\344\270\213\351\231\215\346\247\213\346\226\207\350\247\243\346\236\220.png" differ
diff --git a/test.sh b/test.sh
index 1c43316..aa60a22 100755
--- a/test.sh
+++ b/test.sh
@@ -23,5 +23,6 @@ assert 41 " 12 + 34 - 5 "
 assert 47 '5+6*7'
 assert 15 '5*(9-6)'
 assert 4 '(3+5)/2'
+assert 10 '-10 + 20'
 
 echo OK