concat(L, A)

The members of list L are concatenated to form the atom A.  For example,

                  concat([abc, def], X)?
                  X = abcdef

                  concat([f, r, e, d, 12], X)?
                  X = fred12

The  members  of  L  must be atoms, integers or real.  If X is instantiated
then its value is compared with the result of the concatenation.
