Jim Kelley wrote:
s11*a1 is not zero. s12*a2 is not zero. How you can assert
that they don't exist is really strange.

Perhaps I just understand the meaning of zero better than you do?

OTOH, perhaps not. If my bank balance is zero, does that
mean there have been zero debits and zero credits over
the entire previous month?
--
73, Cecil http://www.w5dxp.com