You can do \beth in TeX, but you need the AMS symbol fonts (msym10 or msbm10) and associated macros (mssymb.tex or some similar name). As a general comment (since I frequently get complaints about mssymb.tex and a4.sty in relation to my diagram macros) if your local TeX system doesn't have these things then you should COMPLAIN LOUDLY to your system manager as they are part of the standard TeX distribution. The same applies if you're still running TeX version 2.993 (I've even seen systems with 2.0 still!): 3.1 is current. TeX is public domain and available from several fileservers; there is really no excuse for having defective systems, especially if you're a unix user.