Question Number 6549 by Rasheed Soomro last updated on 01/Jul/16
$${A}\:{table}\:{with}\:{three}\:{legs}\:{sits}\:{smoothly} \\ $$$${on}\:{every}\:{kind}\:{of}\:{surface},\:{whereas}\:{a} \\ $$$${table}\:{with}\:{four}\:{legs}\:{may}\:{not}\:{sit}\:{on} \\ $$$${rough}\:{surface}.\:{Why}? \\ $$