public Builder<T> lparen(final T lparen) {
			return lparen(token -> Objects.equals(token, lparen));
		}
Set the <em>prototype</em> for the {@code lparen} token. A given
token is treated as  {@code lparen} if {@code Objects.equals(token, lparen)}
returns {@code true}.

@param lparen the {@code lparen} prototype
@return {@code this} builder, for method chaining
jenetics.ext/src/main/java/io/jenetics/ext/internal/util/FormulaParser.java