public Builder<T> functions(final Set<? extends T> functions) {
			return functions(Set.copyOf(functions)::contains);
		}
Set all functions tokens.

@param functions the function tokens
@return {@code this} builder, for method chaining
@throws NullPointerException if the {@code functions} is {@code null}
jenetics.ext/src/main/java/io/jenetics/ext/internal/util/FormulaParser.java