Checks whether a topology exists.
(tpm_acexist toponame [source [loaded]])
Returns T if the topology exists or nil.
| toponame | Topology name (string) |
| source | Source flag T or nil: T Check topologies in the current and source drawings nil Check the current drawing only (default) |
| loaded | Loaded in memory flag T or nil: T Check only topologies in memory nil Check all topologies (default) |