[NetLogo] Runtime error

Bonjour,

je suis entrain de tester NetLogo, j'ai voulu voir ce code mais j'obtiens cette erreur
j'ai crée un bouton
command : setup
Agent(s): observer

Code:

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breed [runners runner] breed [halos halo] to setup clear-all set-default-shape halos "thin ring" create-runners 10 [ setxy random-xcor random-ycor ] reset-ticks end ;to go ; ask runners [ fd 0.1 ] ; tick ;end

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Runtime Error

Code:

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"thin ring" is not a currently defined turtle shape. error while observer running SET-DEFAULT-SHAPE called by procedure SETUP called by Button 'setup'

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