Jerzy Łoś (March 22, 1920-June 1, 1998) (pronounced [jɛʐɨ wɔɕ]) was a Polish mathematician, logician, economist, and philosopher. He is best known for his work on ultraproducts, in particular for " Łoś' theorem", which states that any first-order formula is true in an ultraproduct if and only if it is true in "most" factors (see ultraproduct for details). In 1996 Łoś suffered from a severe brain stroke. He was thenceforward ill until his death in 1998.
