An SMT solver used by the Axe toolkit
STP is an SMT solver available here.
It is used by several tools in the Axe toolkit. See build::cert_param for
information on suppressing attempts to use STP during builds.
Different versions of STP support different option syntax, especially for the max conflicts option, so you might need to set the environment variable ACL2_STP_VARIETY. The default (equivalent to a setting of "2") should work with the latest STP and with other versions that use the option --max-num-confl (note the dashes). For older STP versions that use the option --max_num_confl (note the underscores), set ACL2_STP_VARIETY to "1". For very old versions of STP that only support the use of -g for the max conflicts option, set ACL2_STP_VARIETY to "0".
To test whether STP is being called correctly in your environment, run the script [books]/kestrel/axe/teststp.bash with no arguments. Its output should include the string "Valid." if STP is being correctly invoked.