European regulators are to push ahead with an antitrust inquiry into IBM’s dominance of the computer mainframe market, in spite of the computer maker’s acquisition this week of the small rival whose complaint had stirred up the review.

On Wednesday, IBM ann­oun­ced it was buying Platform Solutions Inc, a Silicon Valley start-up which had been trying to enter the main­frame computer business. PSI had been pursuing an antitrust suit ag­ainst IBM in the US and had complained to European competition regulators. It withdrew the latter ob­­jection on Wed­nesday, just before the IBM deal, for an un­­­named sum, was disclosed.