THE LOGIC NOTES

Tableau exercises More about first Order logic

The following sequents provide practice in the art of constructing tableaux. Answers are given, but of course the idea is to come up with solutions of your own before looking them up. As ever, the answers are not unique: in some cases, alternative tableaux are just as good as the ones given.


ALLx (Fx IMP Gx),   ⊢   NOTSOMEx (Fx AND NOTGx) Try it Answer
NOTSOMEx (Fx AND NOTGx)   ⊢   ALLx (Fx IMP Gx) Try it Answer
ALLx (Fx IMP Gx),  SOMEx (Gx AND Hx)   ⊢   SOMEx (Fx AND Hx) Try it Answer
ALLx (Fx IMP Gx),  ALLx (Gx IMP Hx)   ⊢   ALLx (Fx IMP Hx) Try it Answer
ALLx (Fx IMP Gx),  SOMEx (Hx AND NOTGx)   ⊢   SOMExNOT(Fx OR NOTHx) Try it Answer
ALLx (Fx IMP Hx),  ALLx (Gx IMP Hx)   ⊢   SOMEx (Fx OR Gx) Try it Answer
SOMExNOTFx OR SOMExGx   ⊢   SOMEx (Fx IMP Gx) Try it Answer
ALLx (Fx OR Gx)   ⊢   ALLxFx OR SOMExGx Try it Answer
SOMExFx AND SOMExGx   ⊢   SOMEx (Fx AND Gx) Try it Answer
ALLxSOMEy Rxy   ⊢   SOMExALLy (Rxy OR Ryx) Try it Answer
ALLx(Fx OR Gx),  ALLx(Gx IMP Hx)   ⊢   ALLx(NOTHx IMP Fx) Try it Answer
ALLxSOMEy Rxy   ⊢   SOMExSOMEy (Rxy AND Ryx) Try it Answer
ALLxALLyALLz((Rxy AND Ryz) IMP Rxz),  ALLxALLy(Rxy IMP Ryx),  ALLxSOMEy Ryx   ⊢   ALLx Rxx Try it Answer
ALLxALLy(Rxy IMP >Sxy),  ALLxALLy(Sxy IMP Syx)   ⊢   ALLxALLy(Rxy IMP Ryx) Try it Answer