1. A demapper for a multiple-input, multiple-output symbol receiver, the demapper comprising: a hypothesis determiner to determine hypotheses values for each of a multiplicity of received symbols; and a first half counter-hypotheses determiner to reuse interim results of said hypothesis determiner to generate a first half of counter-hypotheses; wherein said hypothesis determiner comprises: a QR decomposer to generate at least an R matrix from an input channel estimate matrix H; wherein the R matrix is an right triangular matrix that has a upper left element r 1 , an upper right element R 12 and a lower right element r 2 ; a normalizer to normalize input signals and elements of said R matrix; a candidate hypothesis generator operating on the output of said normalizer to generate a plurality of constrained candidate hypothesis values for one of said received symbols and resultant unconstrained hypothesis values for a second one of said received symbols; a normalized error calculator to operate with minimal multiplications and to generate an error magnitude for each of said plurality of constrained candidate hypotheses and their resultant unconstrained hypothesis values; and a hypothesis generator to review said error magnitudes and to select a constrained hypothesis and resultant unconstrained hypothesis corresponding to a smallest error magnitude.