diff --git a/main.go b/main.go
index 5b82e03..5513aab 100644
--- a/main.go
+++ b/main.go
@@ -109,19 +109,19 @@ func shuntingYard(re string) []postfixNode {
 				outQueue = append(outQueue, newPostfixNode(whitespaceChars...))
 			case 'S': // Non-whitespace - I am doing this in a fancy way, generating all dot characters, then removing whitespace characters from it
 				outQueue = append(outQueue, newPostfixNode(slices.DeleteFunc(dotChars(), func(r rune) bool {
-					return !slices.Contains(whitespaceChars, r)
+					return slices.Contains(whitespaceChars, r)
 				})...))
 			case 'd': // Digits
 				outQueue = append(outQueue, newPostfixNode(digitChars...))
 			case 'D': // Non-digits - same fancy way as 'S'
 				outQueue = append(outQueue, newPostfixNode(slices.DeleteFunc(dotChars(), func(r rune) bool {
-					return !slices.Contains(digitChars, r)
+					return slices.Contains(digitChars, r)
 				})...))
 			case 'w': // word character
 				outQueue = append(outQueue, newPostfixNode(wordChars...))
 			case 'W': // Non-word character - same fancy way as 'S' and 'D'
 				outQueue = append(outQueue, newPostfixNode(slices.DeleteFunc(dotChars(), func(r rune) bool {
-					return !slices.Contains(wordChars, r)
+					return slices.Contains(wordChars, r)
 				})...))
 			default: // None of the above - append it as a regular character
 				outQueue = append(outQueue, newPostfixCharNode(re_postfix[i]))