private static boolean matches(final Tree<?, ?> node) {
		return
			!(node.value() instanceof Val) &&
			!(node.value() instanceof Var) &&
			node.childStream()
				.allMatch(child -> child.value() instanceof Val);
	}
Return the operation type this rewriter is working on.

@return the operation type this rewriter is working on
jenetics.prog/src/main/java/io/jenetics/prog/op/ConstRewriter.java