Often a succinct search will yield the information one is looking for. Two good places to search include the documentation and the user forums/MathGroup archives.
The following Google search string will find, due to the structure of WRI's website, information about the function NVariationalBound:
NVariationalBound site:documents.wolfram.com inurl:mathematica
The following Google search string will find information about asserting variable assumptions inside the user forum and MathGroup archives:
I hope that users who want to help other users in real time will list themselves here.
Chris ChiassonLucB can be contacted as "MaxisLuc" on skype (http://www.skype.com)
When no one is listed here, you might want to use one of the following distribution list that provide support for mathematica:
email@example.com (GROupe des Utilisateurs de Mathematica Franšais)
or contact directly Wolfram Research at firstname.lastname@example.org.