How do I remove duplicate subgoals in Isabelle? -

in isabelle, 1 reaches scenario there duplicate subgoals. example, imagine following proof script:

lemma "a ∧ a"   apply (rule conji) 

with goals:

proof (prove): step 1  goal (2 subgoals):  1.  2.     

is there way eliminate duplicate subgoal in-place, proofs need not repeated?

the ml-level tactic distinct_subgoals_tac in pure/tactic.ml removes duplicate subgoals, , can used follows:

lemma "a ∧ a"   apply (rule conji)   apply (tactic {* distinct_subgoals_tac *}) 

leaving:

proof (prove): step 2  goal (1 subgoal):  1. 

there not appear way without dropping ml world, unfortunately.