<<< tex \sum_{\substack{ 0>> native [ EUnder True (ESymbol Op "\8721") (EArray [ AlignCenter ] [ [ [ EGrouped [ ENumber "0" , ESymbol Rel "<" , EIdentifier "i" , ESymbol Rel "<" , EIdentifier "m" ] ] ] , [ [ EGrouped [ ENumber "0" , ESymbol Rel "<" , EIdentifier "j" , ESymbol Rel "<" , EIdentifier "n" ] ] ] ]) , EIdentifier "P" , ESymbol Open "(" , EIdentifier "i" , ESymbol Pun "," , EIdentifier "j" , ESymbol Close ")" ]