Given a target program P with input I, the trace set 
contains all traces of the program. By fixing the target machine
and the execution environment of the target program, we can
isolate one trace, which a simulator for the program can consider
its goal to reproduce. This trace is called the ideal target trace.
In an execution of the simulator, the predicted
execution trace of the target program is called a target trace.
An execution trace of the simulator itself
is a simulator trace
.