这是程序代码，我运行了怎么出错呢？

FFFTS02.OBJ : error LNK2005: _F@4 already defined in FFFTS0.OBJ
FFFTS02.OBJ : error LNK2005: _MAIN__ already defined in FFFTS0.OBJ
FFFTS02.OBJ : error LNK2005: _F already defined in FFFTS0.OBJ
Debug/FFFTS0.exe : fatal error LNK1169: one or more multiply defined symbols found
Error executing link.exe.
请大牛指导一下。谢谢啊

EXTERNAL F
DOUBLE PRECISION F,A,B,T
A=0.0
B=1.0
EPS=0.000001
CALL FFFTS(A,B,F,EPS,T)
WRITE(*,10) T
10 FORMAT(1X,'T=',D15.6)
END

FUNCTION F(X)
DOUBLE PRECISION F,X
F=EXP(-X*X)
RETURN
END



SUBROUTINE FFFTS(A,B,F,EPS,T)
DOUBLE PRECISION A,B,F,T,FA,FB,H,T1,S,X
FA=F(A)
FB=F(B)
N=1
H=B-A
T1=H*(FA+FB)/2.0
5 S=0.0
DO 10 K=0,N-1
  X=A+(K+0.5)*H
  S=S+F(X)
10 CONTINUE
T=(T1+H*S)/2.0
IF (ABS(T1-T).GE.EPS) THEN
  T1=T
  N=N+N
  H=H/2.0
  GOTO 5
END IF
RETURN
END