Conflict

Conflict:to come into collision or disagreement; be contradictory, at variance, or in opposition; clash: 

Example:

The account  of  one  eyewitness  conflicted  with  that  of  the  other. My  class  conflicts  with  <span class="hwc" id="hotword" name="hotword" style="font-style:italic;font-family:Georgia,Verdana,Arial,Helvetica,sans-serif;font-size:small;line-height:normal;color:rgb(51,51,51);">my  <span class="hwc" id="hotword" name="hotword" style="font-style:italic;font-family:Georgia,Verdana,Arial,Helvetica,sans-serif;font-size:small;line-height:normal;color:rgb(51,51,51);">going  <span class="hwc" id="hotword" name="hotword" style="font-style:italic;font-family:Georgia,Verdana,Arial,Helvetica,sans-serif;font-size:small;line-height:normal;color:rgb(51,51,51);">to  <span class="hwc" id="hotword" name="hotword" style="font-style:italic;font-family:Georgia,Verdana,Arial,Helvetica,sans-serif;font-size:small;line-height:normal;color:rgb(51,51,51);">the concert