-type instance IsExpr (TrendOp vn e) = IsVarName vn :&&: IsExpr e
-type instance IsCommonExpr (TrendOp vn e) = IsVarName vn :&&: IsCommonExpr e
-type instance MentionedVars (TrendOp vn e) = vn :*: MentionedVars e
+type instance IsExpr (TrendOp vn e) = IsVarName vn :&&: IsExpr e
+type instance IsCommonExpr (TrendOp vn e) = IsVarName vn :&&: IsCommonExpr e
+type instance IsIterativeExpr (TrendOp vn e) = IsVarName vn :&&: IsIterativeExpr e
+type instance MentionedVars (TrendOp vn e) = vn :*: MentionedVars e