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function pesel_check(el) {
	var pesel_waga = '13791379131';
	var pesel_suma = 0;
	if (el.value.length = 11) {
		for (a = 0; a <= 10; a++)
			pesel_suma = pesel_suma + (el.value.substr(a, 1) * pesel_waga.substr(a, 1));

		pesel_suma_str = pesel_suma.toString();

		if (pesel_suma_str.substr(-1, 1) == '0') {
			return true;
		} else {
			el.errors.push("Nieprawidłowy numer PESEL");
			return false;
		}
	}
}