OR notification in SOLR metadata for facets

Question

We are working on Apache solr engine integration with IBM WCS. On applying multiple facets on the pages the previous facets will be converted to some encoded form using Base64 algorithm.

i.e When we will apply three facets F1, F2 and F3, first two F1 and F2 will be encoded and added to metaData field of URL param. and third parameter F3 will go into facet param. and those two previous facets F1 and F2 will be AND'ed using some special character in SOLR. That special character is something line below, <MT@SP>

F1 <MT@SP> F2

May i know what is the similar charater with which i can do logical OR? Like

F1 OR F2???????