An abstract machine based experimental system for a lazy narrowing calculus.

Process for upgrading an olefinic C4 cut issued from a cracking or steam cracking unit, comprising subjecting said cut to isomerization conditions so as to convert at least 80% of its 1-butene content to 2-butenes, subjecting the so-treated C4 cut to polymerization conditions so as to convert at least 90% of its isobutene content to isobutene dimers and trimers without substantially converting the normal butenes, separating the isobutene dimers and trimers, alkylating the remaining fraction and fractionating the latter to an alkylate, L P G and an isobutane containing fraction.