``...it has not been possible to determine why he made the mistake of believing that the fault lay with the No. 2 engine. When asked which engine was at fault he half-formed the word 'left' before saying 'right'. His hesitation may have arisen from genuine difficulty in interpreting the readings on the engine instruments or it may have been that he observed the instruments only during the 6 second period of relative stability between the second and third stages.'' (page 97)

exists t,forall t' :
input(first_officer, throttle_back(engine_2), t) <- observe(first_officer, pei(engine_1), t') v observe(first_officer, pei(engine_2), t')) ^ before(20_05_10, t') ^ before(t', 20_05_16) ^ before(t', t) (6)

• Hypothesis 2:
  - did observe during quiesence.