can often save an afternoon in the library. I seem to have convinced myself that the probability that an nxn bitmatrix will have (mod 2) rank = k is 2 n - k + 1 k + 1 (n - k) (p ; p) (p ; p) p k n - k P(n,k) := -------------------------------------------, (p; p) n - k if the entries are 1 with probability p. Thus the peculiar base p identity Sum P(n,k) = 1. k In particular, the probability of being nonsingular is just (p;p)_n. Can someone tell me whose wheel I have reinvented? --rwg PS to anyone still running my Macsyma ehancements: Is ROW_REDUCE a no-op? It was on my machine until I replaced (defun $row_reduce (x) ...) with (define-autoload "c:\\rwg\\climax\\algebra\\matrix" $row_reduce) in /macsyma/macsyma2/system/init.lsp .