pragma solidity >=0.4.21   <0.6.0;
pragma solidity >=0.4.21 <=0.6.0    ;
pragma solidity    >0.4.21 <0.6.0;
pragma solidity >0.4.21 <=0.6.0;
pragma solidity >=0.4.21<0.6.0;
pragma solidity   ^ 0.4.21  ;
pragma solidity  ~ 0.4.21  ;