a$="1001110011"+#CRLF$+"1110111011"+#CRLF$+"0010010010"+#CRLF$+"1010101010"+#CRLF$+"1111111111"+#CRLF$+
   "0100101101"+#CRLF$+"0100100"   +#CRLF$+"101"       +#CRLF$+"11"        +#CRLF$+"00"        +#CRLF$+
   "1"         +#CRLF$

OpenConsole()

Procedure isRepStr(s1$,s2$)
  If Int(Len(s1$)/Len(s2$))>=2 : ProcedureReturn isRepStr(s1$,s2$+s2$)                         : EndIf
  If Len(s1$)>Len(s2$)         : ProcedureReturn isRepStr(s1$,s2$+Left(s2$,Len(s1$)%Len(s2$))) : EndIf
  If s1$=s2$                   : ProcedureReturn #True : Else : ProcedureReturn #False         : EndIf
EndProcedure

For k=1 To CountString(a$,#CRLF$)
  s1$=StringField(a$,k,#CRLF$) : s2$=Left(s1$,Len(s1$)/2)
  While Len(s2$)
    r=isRepStr(s1$,s2$)
    If Not r : s2$=Left(s2$,Len(s2$)-1) : Else : Break : EndIf
  Wend
  If Len(s2$) And r : PrintN(LSet(s1$,15,Chr(32))+#TAB$+"longest sequence: "+s2$) : EndIf
  If Not Len(s2$)   : PrintN(LSet(s1$,15,Chr(32))+#TAB$+"found nothing.")         : EndIf
Next
Input()