Clarify syntax of next operator
Neither X nor N works as the next operator. Which letter/symbol(s) represent this operator?
X:
property p_EX = E(X(a == 3));
test_properties.modest:(X,19): error: Expected identifier.
test_properties.modest:(X,19): error: Expected ")".
N:
property p_EN = E(N(a == 3));
test_properties.modest:(X,19): error: Use of undefined symbol "N".