referencing mupdf in Qt4 project

Question

I have libfitz.a and libmupdf.a in /usr/local/lib (previously compiled). then I included the headers:

#include <fitz.h>
#include <mupdf.h>

then I put:

INCLUDEPATH  +=/home/pc/sviluppo/mupdf-0.9
INCLUDEPATH  +=/home/pc/sviluppo/mupdf-0.9/fitz
INCLUDEPATH  +=/home/pc/sviluppo/mupdf-0.9/pdf

LIBS         += -L/usr/local/lib -lfitz
LIBS         += -L/usr/local/lib -lmupdf

in .pro file, but my program just reaches to types in the headers, not the library. The error is

/.../mainwindow.cpp:-1: error: undefined reference to `pdf_open_xref(pdf_xref_s**, char const*, char*)'

What's wrong?