diff -r 259e3a90ad97 -r 8db773f19586 lemon/preflow.h
--- a/lemon/preflow.h	Thu Mar 22 18:56:26 2018 +0100
+++ b/lemon/preflow.h	Thu Mar 22 18:56:47 2018 +0100
@@ -476,7 +476,7 @@
     /// Initializes the internal data structures and sets the initial
     /// flow to the given \c flowMap. The \c flowMap should contain a
     /// flow or at least a preflow, i.e. at each node excluding the
-    /// source node the incoming flow should greater or equal to the
+    /// source node the incoming flow should be greater or equal to the
     /// outgoing flow.
     /// \return \c false if the given \c flowMap is not a preflow.
     template <typename FlowMap>
@@ -495,7 +495,7 @@
         for (OutArcIt e(_graph, n); e != INVALID; ++e) {
           excess -= (*_flow)[e];
         }
-        if (excess < 0 && n != _source) return false;
+        if (_tolerance.negative(excess) && n != _source) return false;
         (*_excess)[n] = excess;
       }
 
@@ -639,7 +639,7 @@
 
           (*_excess)[n] = excess;
 
-          if (excess != 0) {
+          if (_tolerance.nonZero(excess)) {
             if (new_level + 1 < _level->maxLevel()) {
               _level->liftHighestActive(new_level + 1);
             } else {
@@ -720,7 +720,7 @@
 
           (*_excess)[n] = excess;
 
-          if (excess != 0) {
+          if (_tolerance.nonZero(excess)) {
             if (new_level + 1 < _level->maxLevel()) {
               _level->liftActiveOn(level, new_level + 1);
             } else {
@@ -791,7 +791,7 @@
       for (NodeIt n(_graph); n != INVALID; ++n) {
         if (!reached[n]) {
           _level->dirtyTopButOne(n);
-        } else if ((*_excess)[n] > 0 && _target != n) {
+        } else if (_tolerance.positive((*_excess)[n]) && _target != n) {
           _level->activate(n);
         }
       }
@@ -852,7 +852,7 @@
 
         (*_excess)[n] = excess;
 
-        if (excess != 0) {
+        if (_tolerance.nonZero(excess)) {
           if (new_level + 1 < _level->maxLevel()) {
             _level->liftHighestActive(new_level + 1);
           } else {