Question: Spider & fly Dudeney problem - a new twist

Hi Please see Spiderflygrid2.mws A spider is on the floor of a cubical room of side 1. Its position is given. Where must the fly position itself to be as far as possible from the spider? My attempt minimizes the square of the twelve possible distances. This is m. m:=min(seq(cd[i], i=1..12)); Partial derivatives of m are found with respect to xf (the x coord of the fly) eq1:=diff(m,xf); ... & with respect to yf (the y coord of the fly) eq2:=diff(m,yf); These two equations are then solved simultaneously. solve({eq1,eq2}); Maple gives an error message - is this due to the discontinuities in the expression m? Or (more likely) a fault in my Maple code? Thanks David
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