Abstract
LetG= SL(2,DOUBLE-STRUCK CAPITAL Z) & x22c9; DOUBLE-STRUCK CAPITAL Z(2)andH= SL(2,DOUBLE-STRUCK CAPITAL Z). We prove that the actionG & x21b7; Double-struck capital R(2)isuniformly non-amenableand that the quasi-regular representation ofGon l(2)(G/H) has auniform spectral gap. Both results are a consequence of a uniform quantitative form of ping-pong for affine transformations, which we establish here.