^{What does this pseudo code mean?}

stackst{1,2,3,4} is not clear. What does it mean?

function CHECKGRIDS(puzzle):

for 0<=i

stackst{1,2,3,4}

for 0<=j

if SEARCHSTACK(st,puzzle[i][j])==FALSE:

return FALSE

end if

end for

end for

return TRUE

end function