@Override
		public String toString() {
			return format("%s%s", VAR_PREFIX, name);
		}
@param name the name of the variable
@throws NullPointerException if the given {@code name} is {@code null}
@throws IllegalArgumentException if the given {@code name} is not a
        valid Java identifier
jenetics.ext/src/main/java/io/jenetics/ext/rewriting/TreePattern.java