theory Tacticals = Main:
text{*REPEAT*}
lemma "\<lbrakk>(P\<longrightarrow>Q); (Q\<longrightarrow>R); (R\<longrightarrow>S); P\<rbrakk> \<Longrightarrow> S"
apply (drule mp, assumption)
apply (drule mp, assumption)
apply (drule mp, assumption)
apply (assumption)
done
lemma "\<lbrakk>(P\<longrightarrow>Q); (Q\<longrightarrow>R); (R\<longrightarrow>S); P\<rbrakk> \<Longrightarrow> S"
by (drule mp, assumption)+
text{*ORELSE with REPEAT*}
lemma "\<lbrakk>(Q\<longrightarrow>R); (P\<longrightarrow>Q); x<#5\<longrightarrow>P; Suc x < #5\<rbrakk> \<Longrightarrow> R"
by (drule mp, (assumption|arith))+
text{*exercise: what's going on here?*}
lemma "\<lbrakk>(P\<and>Q\<longrightarrow>R); (P\<longrightarrow>Q); P\<rbrakk> \<Longrightarrow> R"
by (drule mp, intro?, assumption+)+
text{*defer and prefer*}
lemma "hard \<and> (P \<or> ~P) \<and> (Q\<longrightarrow>Q)"
apply intro --{* @{subgoals[display,indent=0,margin=65]} *}
defer 1 --{* @{subgoals[display,indent=0,margin=65]} *}
apply blast+ --{* @{subgoals[display,indent=0,margin=65]} *}
oops
lemma "ok1 \<and> ok2 \<and> doubtful"
apply intro --{* @{subgoals[display,indent=0,margin=65]} *}
prefer 3 --{* @{subgoals[display,indent=0,margin=65]} *}
oops
(*needed??*)
lemma "(P\<or>Q) \<and> (R\<or>S) \<Longrightarrow> PP"
apply elim
oops
lemma "((P\<or>Q) \<and> R) \<and> (Q \<and> (P\<or>S)) \<Longrightarrow> PP"
apply (elim conjE)
oops
lemma "((P\<or>Q) \<and> R) \<and> (Q \<and> (P\<or>S)) \<Longrightarrow> PP"
apply (erule conjE)+
oops
end