diff --git a/term.go b/term.go
index 556410f..457e1c2 100644
--- a/term.go
+++ b/term.go
@@ -62,8 +62,8 @@ func (s *term) Clone() (d *term) {
 		}
 	}
 	d = &term{
-		tk: *s.tk.Clone(),
-		parent: s.parent,
+		tk:       *s.tk.Clone(),
+		parent:   s.parent,
 		children: children,
 		position: s.position,
 		priority: s.priority,
@@ -211,11 +211,11 @@ func (term *term) checkOperands() (err error) {
 		}
 	case posPrefix:
 		if term.children == nil || len(term.children) != 1 || term.children[0] == nil {
-			err = term.tk.Errorf("prefix operator %q requires one not nil operand", term.tk.String())
+			err = term.tk.Errorf("prefix operator %q requires one non-nil operand", term.tk.String())
 		}
 	case posPostfix:
 		if term.children == nil || len(term.children) != 1 || term.anyChildrenNil() {
-			err = term.tk.Errorf("postfix operator %q requires one not nil operand", term.tk.String())
+			err = term.tk.Errorf("postfix operator %q requires one non-nil operand", term.tk.String())
 		}
 	case posMultifix:
 		if term.children == nil || len(term.children) < 3 || term.anyChildrenNil() {