Mika often says how convenient he finds the Dictionary lookup integrated in Safari. I do not know how well that performs on mathematical terms so I tested it and compared it briefly with the wikilook plugin. To make a story short: Dictionary lookup finds terms that wikilook fails to parse. They both resort to checking Wikipedia but one finds combined terms such as ''rational functions'' while the other does not, not yet at least. None of them is able to handle numerical expressions such as the geometric series ''1/2 + 1/4 + 1/8 + ...'', which is on Wikipedia and Google can find.