VHImpUmat.f:476:20:

  sv%Fm = get_Fm(T)                                                 !     $F_M(Tb)$ limit stress obliquity (depends on $theta$)
               1
Error: Return type mismatch of function ‘get_fm’ at (1) (UNKNOWN/REAL(8))
AVHImpUmat.f:476:14:

  sv%Fm = get_Fm(T)                                                 !      $F_M(Tb)$ limit stress obliquity (depends on $theta$)
          1
Error: Function ‘get_fm’ at (1) has no IMPLICIT type

subroutine stiffness_and_derivatives(T,sv,mat,d,msg)
  use tools_lt
  use constitutive_names
  implicit none
  type (MATERIALCONSTANTS),intent(in) :: mat
  type (STATEVARIABLES),intent(inout) :: sv
  type (DERIVATIVES), intent(inout) :: d
  type (MESSAGE),intent(inout) :: msg
  character*40 :: whereIam
  real(8), intent(in) :: T(3,3)
  real(8), dimension(3,3,3,3,3,3) :: c,ctransp
  real(8) :: trT3,fac

  sv%Fm = get_Fm(T)                                                 !   $F_M(Tb)$ limit stress obliquity (depends on $theta$)
  sv%That = hated(T)                                                !    $hat {Tb} = Tb / tr Tb$
  sv%LLhat= sv%Fm*sv%Fm*Idelta+mat%az2*(sv%That .out. sv%That)      !   linear hp stiffness $ hat{cE} = a^2 left[ left(Frac{F_M}{a}right)^2 cI + hTb hTb right] $
  sv%LL   = -( sv%trT/(3.0d0*mat%Cs) )* sv%LLhat                    !   $ cE = frac{-trTb}{3 kappa} hat{cE}$
!----- dLLhatdT ----------
  trT3 = sv%trT**3                                                  !    $tr^3 Tb$
  fac =  mat%az2 / trT3
  c = (Idelta .out. T)                                              !   $c_{ijmnkl}= I_{ijmn}T_{kl}$
  ctransp = tpose35i46(c)                                           !   $c^T= c_{ijklmn}$
  d%dLLhatdT = fac * ( sv%trT*ctransp + sv%trT*(T .out. Idelta)
 &              - 2.0d0*( T .out. ( T .out. delta) ) )              !    $ hat E_{ijklmn}'=a^2left(dfrac{ T_{rr} I_{ijmn}T_{kl} + T_{rr} T_{ij}I_{klmn}-2  T_{ij}T_{kl} delta_{mn} }{ (T_{rr})^3}    +  2 dfrac{F_M}{a} I_{ijkl}F'_{M, mn}  right)$
                                                                    !    $F'_M approx 0$ is assumed
  d%dLLdT = -(1.0d0/(3.0d0*mat%Cs) )*((sv%LLhat .out. delta)        !   $cE_{ }' = frac{-1}{3 kappa}  hatcE oneb + dfrac{-tr Tb}{3kappa}hatcE'$
 &              + sv%trT*d%dLLhatdT )
end subroutine stiffness_and_derivatives

real(8) :: get_fm