This section provides predicates for atom processing.
Length of an atom.
atom_length(Atom, Length) is true if and only if the number of characters in the name of Atom is equal to Length. If Length is not instantiated, atom_length will calculate the length of Atom's name.
atom_concat(Start, End, Whole) is true if and only if Whole is the atom obtained by adding the characters of End at the end of Start. If Whole is the only argument instantiated, atom_concat/3 will obtain all possible decompositions of it.